Multiple objectives metrology system, lithographic apparatus, and methods thereof

A method comprising:

• splitting an illumination beam into a first sub-beam and a second sub-beam using a non-polarizing beam splitter comprising four quadrants comprising a first pair of mirrored quadrants and a second pair of non-mirrored quadrants;
• directing, via the first pair of mirrored quadrants of the non-polarizing beam splitter, the first sub-beam to a first spot on a substrate, wherein the substrate includes one or more target structures;
• directing, via the second pair of non-mirrored quadrants of the non-polarizing beam splitter, the second sub-beam to a second spot on the substrate, wherein the first spot is a different location than the second spot;
• recombining, using an optical element, diffracted beams from the first and second spots;
• generating, at a detector, a detection signal based on the recombining;
• and
• analyzing the detection signal to determine a property of the one or more target structures based on at least the detection signal.

A lithography apparatus comprising:

• an illumination apparatus configured to illuminate a pattern of a patterning device;
• a projection system configured to project an image of the pattern onto a substrate;
• and
• a metrology or inspection system comprising:
• an illumination system configured to generate an illumination beam,
• a non-polarizing beam splitter configured to split the illumination beam into a first sub-beam and a second sub-beam, wherein the non-polarizing beam splitter comprises four quadrants comprising a first pair of mirrored quadrants and a second pair of non-mirrored quadrants,
• a first optical device configured to receive the first sub-beam via the first pair of mirrored quadrants of the non-polarizing beam splitter and direct the first sub-beam towards a first spot on a substrate, the substrate having one or more target structures,
• a second optical device configured to receive the second sub-beam via the second pair of non-mirrored quadrants of the non-polarizing beam splitter and direct the second sub-beam towards a second spot on the substrate, wherein the first spot is a different location than the second spot,
• an optical element configured to receive diffracted beams from the first and second spots and recombine the diffracted beams;
• a detector configured to receive recombined diffracted beams from the optical element and to generate a detection signal, and
• a processor configured to analyze the detection signal to determine a property of the one or more target structures based on at least the detection signal.